Vertically aligned carbon nanotube arrays as electrodes

ABSTRACT

Embodiments of the present disclosure pertain to electrodes that include a plurality of vertically aligned carbon nanotubes and a metal associated with the vertically aligned carbon nanotubes. The vertically aligned carbon nanotubes may be in the form of a graphene-carbon nanotube hybrid material that includes a graphene film covalently linked to the vertically aligned carbon nanotubes. The metal may become reversibly associated with the carbon nanotubes in situ during electrode operation and lack any dendrites or mossy aggregates. The metal may be in the form of a non-dendritic or non-mossy coating on surfaces of the vertically aligned carbon nanotubes. The metal may also be infiltrated within bundles of the vertically aligned carbon nanotubes. Additional embodiments pertain to energy storage devices that contain the electrodes of the present disclosure. Further embodiments pertain to methods of forming said electrodes by applying a metal to a plurality of vertically aligned carbon nanotubes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/151,941, filed on Apr. 23, 2015. The entirety of theaforementioned application is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant No.FA9550-12-1-0035, awarded by the U.S. Department of Defense; and GrantNo. FA9550-14-1-0111, awarded by the U.S. Department of Defense. Thegovernment has certain rights in the invention.

BACKGROUND

Current electrodes suffer from numerous limitations, including limitedmetal storage capacities, and the formation of dendritic materialsduring operation. Various aspects of the present disclosure address theaforementioned limitations.

SUMMARY

In some embodiments, the present disclosure pertains to electrodes thatinclude a plurality of vertically aligned carbon nanotubes and a metalassociated with the vertically aligned carbon nanotubes. In someembodiments, the vertically aligned carbon nanotubes include verticallyaligned single-walled carbon nanotubes that are in the form of an array.In some embodiments, the vertically aligned carbon nanotubes areassociated with a substrate. In some embodiments, the substrate servesas a current collector. In some embodiments, the vertically alignedcarbon nanotubes and the substrate serve as a current collector.

In some embodiments, the vertically aligned carbon nanotubes are in theform of a graphene-carbon nanotube hybrid material, where the verticallyaligned carbon nanotubes are covalently linked to the graphene filmthrough carbon-carbon bonds at one or more junctions between the carbonnanotubes and the graphene film. In some embodiments, the graphene filmis also associated with a substrate, such as a copper or nickelsubstrate.

The vertically aligned carbon nanotubes of the present disclosure may beassociated with various metals. For instance, in some embodiments, themetal includes, without limitation, alkali metals, alkaline earthmetals, transition metals, post transition metals, rare-earth metals,and combinations thereof. In some embodiments, the metal includes,without limitation, Li, Na, K, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,Zn, Al, Sn, Sb, Pb, and combinations thereof. In some embodiments, themetal includes lithium.

In some embodiments, the metal becomes reversibly associated with thevertically aligned carbon nanotubes in situ during electrode operation.In some embodiments, the metal associated with the vertically alignedcarbon nanotubes lacks any dendrites or aggregates (e.g., mossyaggregates). In some embodiments, the metal is in the form of anon-dendritic or non-mossy coating on surfaces of the vertically alignedcarbon nanotubes. In some embodiments, the metal is infiltrated withinbundles of the vertically aligned carbon nanotubes.

In some embodiments, the vertically aligned carbon nanotubes serve asthe active layer of the electrode. In some embodiments, the metals serveas the active layer of the electrode while the vertically aligned carbonnanotubes serve as a current collector (either alone or in conjunctionwith a substrate). In some embodiments, the electrode is an anode or acathode. In some embodiments, the electrode is a component of an energystorage device, such as a lithium-ion battery or a lithium-ioncapacitor.

Additional embodiments of the present disclosure pertain to energystorage devices that contain the electrodes of the present disclosure.Further embodiments of the present disclosure pertain to methods offorming the electrodes of the present disclosure.

DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the formation of electrodes (FIG. 1A), a structure ofa formed electrode (FIG. 1B), and the use of the formed electrodes in abattery (FIG. 1C).

FIG. 2 illustrates the growth and structural characterization ofgraphene-carbon nanotube hybrid materials (GCNTs). FIG. 2A provides aschematic of GCNT growth. E-beam deposited 1 nm iron nanoparticles werenon-continuous and they served as the catalysts for the carbon nanotube(CNT) growth while a 3 nm layer of aluminum oxide provided the supportfor a vertical growth. FIGS. 2B-D provide scanning electron microscopy(SEM) images of GCNT showing a CNT carpet grown vertically from agraphene-covered copper (Cu) substrate. FIG. 2E shows a Raman spectrumof graphene as-grown on Cu. The graphene is conformally connected to itsnative Cu substrate upon which it is grown. The G band appears at 1589cm⁻¹ while the 2D band appears at 2705 cm⁻¹ to provide an I_(G)/I_(2D)ratio of more than 1. A trace D band appears at ˜1360 cm⁻¹. The Ramanscattering signatures signify a high quality multilayer graphene. Theskewed baseline occurred because the spectrum is obtained atop Cu. FIG.2F provides a Raman spectrum of CNTs grown on the Cu-graphene substratewith the G band at 1587 cm⁻¹, the 2D band at 2652 cm⁻¹, and the D bandat 1336 cm⁻¹. FIG. 2G provides a Raman radial breathing mode (RBM)spectrum of the CNTs in expanded format.

FIG. 3 illustrates the morphology of GCNT associated with lithium(GCNT-Li). FIG. 3A provides a schematic of GCNT-Li formation. FIG. 3Bprovides voltage vs. time of lithiation and delithiation processes ofGCNT-Li. FIG. 3C provides a photograph of GCNTs, GCNT-Li, anddelithiated GCNT-Li (scale bar corresponds to 1 cm). SEM images ofGCNT-Li (0.7 mAh cm⁻² at 2 mA cm⁻²) after 250 cycles are shown through atop-view (FIG. 3D), side-view (FIG. 3E), expanded top-view (FIG. 3F),and expanded side-view (FIG. 3G). SEM images of de-lithiated GCNT-Li arealso shown through a top-view (FIG. 3H) and an expanded top-view (FIG.3I). Transmission electron microscopy (TEM) images of a CNT from GCNT-Li(FIG. 3J) and its higher magnification (FIG. 3K) are also shown. FIG. 3Lshows a schematic of Li deposited on graphene grown on Cu. FIG. 3Mprovides an SEM image of Li deposited directly on graphene grown on Cufoil (0.7 mAh cm⁻² at 2 mA cm⁻²) without GCNT, showing the mossy anddendritic Li deposition, especially at higher magnification (FIG. 3N).

FIG. 4 provides electrochemical characteristics of GCNT-Li anodes. FIG.4A shows the charge/discharge profile of GCNT-Li. Gravimetric capacityis based on the mass of GCNT, measured on a microbalance after CNTgrowth. FIG. 4B shows a voltage profile of GCNT over 200 hours,corresponding to 300 charge-discharge cycles. FIG. 4C provides a voltageprofile of Cu-Li over 160 hours, corresponding to 250 charge-dischargecycles. FIG. 4D provides cycle performance and coulombic efficiency ofGCNT-Li. The current density is 2 mA cm⁻²(12 A g⁻¹ _(GCNT)).

FIG. 5 shows the first cycle charge/discharge profile of Li metaldeposited on copper-graphene (CuG) materials (CuG-Li).

FIG. 6 shows the charge/discharge profile of GCNT-Li.

FIG. 7 shows the voltage characteristics of GCNT-Li anodes.Charge/discharge voltage profiles of GCNT-Li for the 6th and 300thcycles are shown. The slightly higher Li extraction time for the 300thcycle corresponds to a slightly higher capacity and increased coulombicefficiency of 99.83% compared to 94.3% for the 6th cycle. The currentdensity is 2 mA cm⁻²(12 A g⁻¹ _(GCNT)).

FIG. 8 compares the electrochemical characteristics of GCNT-based anodeswith horizontal CNT-based anodes. FIG. 8A shows the schematics andvoltage profiles of vertical and seamless GCNT grown on Cu. FIG. 8Bshows the schematics and voltage profiles of horizontal CNT deposited ongraphene-covered Cu.

FIG. 9 shows data relating to Li storage and rate capabilities ofGCNT-Li anodes. FIG. 9A shows the Li storage capacities of GCNTs from0.4 to 4 mAh cm⁻². Comparison of the gravimetric capacity of GCNTs withother anode materials with respect to the mass of the anode (FIG. 9B)and the mass of the anode and Li inserted (FIG. 9C) are also shown. Theareal capacities of GCNT-Li from 0.4 to 4 mAh cm⁻² are represented byGCNT-Li-0.4 to GCNT-Li-4. FIG. 9D shows the charge-discharge profilesmeasured at different current densities expressed in current density perarea and per mass of electrode. FIG. 9E shows the cycle performance ofGCNT-Li measured at different current densities.

FIG. 10 shows the volumetric capacities of GCNT-Li anodes with arealcapacity from 0.4 to 4 mAh cm⁻². Despite the very low density of GCNTs(35 mg/cm³), the GCNT is capable of storing large amounts of Li on thesurfaces of the CNTs without Li particulate formation in the large(micrometer-scale) pores of the material.

FIG. 11 shows the electrochemical characteristics of prelithiated GCNTs.FIG. 11A shows the voltage profile of GCNTs during Li insertion. FIG.11B shows the voltage profile of GCNTs during Li extraction followed byLi insertion up to 1 mAh cm⁻². The excess Li remains in the GCNT. FIG.11C shows cycle performance of GCNT-Li with excess Li. FIG. 11D showscoulombic efficiency of GCNT-Li with and without excess Li.

FIG. 12 shows the electrochemical performance of a full battery thatcontains GCNT-Li as the anode and sulfur/carbon black as the cathode.The charge-discharge profiles of the first three cycles of the batterywere measured. The electrochemical performance of the battery isexpressed in terms of gravimetric capacity (mass of S and mass ofinserted Li). The two plateau are related to high order and low orderlithium polysulfide (Li_(x)S_(y)) formation.

FIG. 13 shows the electrochemical performance of a full battery thatcontains GCNT-Li as the anode and lithium cobalt oxide (LiCoO₂) as thecathode. The charge-discharge profiles of the first two cycles of thefull battery were measured.

DETAILED DESCRIPTION

It is to be understood that both the foregoing general description andthe following detailed description are illustrative and explanatory, andare not restrictive of the subject matter, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one”, and the use of “or” means “and/or”, unlessspecifically stated otherwise. Furthermore, the use of the term“including”, as well as other forms, such as “includes” and “included”,is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that comprise more than one unit unless specifically statedotherwise.

The section headings used herein are for organizational purposes and arenot to be construed as limiting the subject matter described. Alldocuments, or portions of documents, cited in this application,including, but not limited to, patents, patent applications, articles,books, and treatises, are hereby expressly incorporated herein byreference in their entirety for any purpose. In the event that one ormore of the incorporated literature and similar materials defines a termin a manner that contradicts the definition of that term in thisapplication, this application controls.

Due to the increased use of energy storage devices in variouselectronics, there has been a need for the development of energy storagedevices with high power densities, high energy densities, and fastcharge/discharge rates. For instance, lithium-ion batteries have beenutilized as energy storage devices due to their high energy and powercapabilities.

In particular, lithium-ion batteries contain high capacity lithium hostmaterials that serve as anodes. Such host materials can include silicon,tin, graphite, and transition metal compounds (e.g., iron oxide).Generally, lithium ions intercalate into the host materials to form analloy. The lithium ions can also become integrated into the hostmaterials by a conversion reaction.

However, the theoretical capacity of lithium ion batteries is limited bythe amount of lithium that can be stored in or reacted with the hostmaterials. For instance, the theoretical capacity of lithium-ionbatteries that contain graphite-based anodes is limited to about 372mAh/g. Likewise, the theoretical capacity of lithium-ion batteries thatcontain iron oxide-based anodes is limited to about 1,007 mAh/g.Similarly, the theoretical capacity of lithium-ion batteries thatcontain silicon-based anodes is limited to about 3,579 mAh/g.

Furthermore, major safety concerns exist when lithium is utilized as ananode component in lithium ion batteries and other energy storagedevices. In particular, safety hazard issues arise due to the formationof dendritic and related structures by the lithium ions, especially athigh current densities. Such dendritic structures are usuallynon-uniform crystals that grow in the form of fiber-like, needle-like,moss-like, or tree-like structures.

The dendritic structures can generate significant volume expansionduring cycling. The volume expansions can in turn diminish an energystorage device's coulombic efficiency and cycle life by blocking theseparator pores and inducing continuous electrolyte decomposition. Sucheffects can in turn lead to internal short circuits. This is especiallydangerous because of the presence of organic solvent components inbatteries.

Various approaches have been utilized to address issues arising fromdendritic growth in energy storage devices. Such approaches haveincluded: (a) new additives and electrolyte salt/solvent combinations toenable formation of a strong and stable solid electrolyte interphase(SEI); (b) coating the electrode with a mechanically strong porouspolymer, solid membrane, or ionic conductor as a separator in order tosuppress or prevent dendritic growth and penetration; and (c) forming aprotective shell on the current collector to encapsulate the lithium andprevent dendritic growth. However, since dendrite formation is morerapid and severe at higher current densities, the aforementionedapproaches can limit lithium storage capacity per unit electrode areaand cycle life. For the same reasons, the aforementioned approaches canrestrict electrode current density.

As such, a need exists for electrodes that exhibit optimal metal storagecapacities and minimal dendrite formation. Various aspects of thepresent disclosure address this need.

In some embodiments, the present disclosure pertains to methods ofmaking electrodes that contain vertically aligned carbon nanotubes. Insome embodiments illustrated in FIG. 1A, the methods of the presentdisclosure include applying a metal to a plurality of vertically alignedcarbon nanotubes (step 10) such that the metal becomes associated withthe vertically aligned carbon nanotubes (step 12). In some embodiments,the methods of the present disclosure also include a step ofincorporating the formed electrode as a component of an energy storagedevice (step 14).

In additional embodiments, the present disclosure pertains to the formedelectrodes. In some embodiments, the electrodes of the presentdisclosure include a plurality of vertically aligned carbon nanotubesand a metal that is associated with the vertically aligned carbonnanotubes. In more specific embodiments illustrated in FIG. 1B, theelectrodes of the present disclosure can be in the form of electrode 30,which includes metal 32, vertically aligned carbon nanotubes 34,graphene film 38, and substrate 40. In this embodiment, verticallyaligned carbon nanotubes 34 are in the form of array 35. The verticallyaligned carbon nanotubes are covalently linked to graphene film 38through seamless junctions 36. In addition, metal 32 is associated withvertically aligned carbon nanotubes 34 in the form of non-dendritic ornon-mossy films.

Further embodiments of the present disclosure pertain to energy storagedevices that contain the electrodes of the present disclosure. Forinstance, as illustrated in FIG. 1C, the electrodes of the presentdisclosure can be utilized as components of battery 50, which containscathode 52, anode 56, and electrolytes 54. In this embodiment, theelectrodes of the present disclosure can serve as cathode 52 or anode56.

As set forth in more detail herein, the present disclosure can utilizevarious types of vertically aligned carbon nanotubes. Moreover, variousmetals may be associated with the vertically aligned carbon nanotubes invarious manners. Furthermore, the electrodes of the present disclosurecan be utilized as components of various energy storage devices.

Vertically Aligned Carbon Nanotubes

The electrodes of the present disclosure can include various types ofvertically aligned carbon nanotubes. For instance, in some embodiments,the vertically aligned carbon nanotubes include, without limitation,single-walled carbon nanotubes, double-walled carbon nanotubes,triple-walled carbon nanotubes, multi-walled carbon nanotubes,ultra-short carbon nanotubes, small diameter carbon nanotubes, pristinecarbon nanotubes, functionalized carbon nanotubes, and combinationsthereof. In some embodiments, the vertically aligned carbon nanotubesinclude vertically aligned single-walled carbon nanotubes.

In some embodiments, the vertically aligned carbon nanotubes of thepresent disclosure include pristine carbon nanotubes. In someembodiments, the pristine carbon nanotubes have little or no defects orimpurities.

In some embodiments, the vertically aligned carbon nanotubes of thepresent disclosure include functionalized carbon nanotubes. In someembodiments, the functionalized carbon nanotubes includesidewall-functionalized carbon nanotubes. In some embodiments, thefunctionalized carbon nanotubes include one or more functionalizingagents. In some embodiments, the functionalizing agents include, withoutlimitation, oxygen groups, hydroxyl groups, carboxyl groups, epoxidemoieties, and combinations thereof.

In some embodiments, the sidewalls of the vertically aligned carbonnanotubes of the present disclosure contain structural defects, such asholes. In some embodiments, carbons at the edges of the structuraldefects (e.g., holes) are terminated by one or more of atoms orfunctional groups (e.g., hydrogen, oxygen groups, hydroxyl groups,carboxyl groups, epoxide moieties, and combinations thereof).

The vertically aligned carbon nanotubes of the present disclosure can bein various forms. For instance, in some embodiments, the verticallyaligned carbon nanotubes are in the form of an array (e.g., array 35 inFIG. 1B). In some embodiments, the array is in the form of a carpet or aforest. In some embodiments, the array is in the form of superlatticesheld together by van der Waals interactions.

In some embodiments, the vertically aligned carbon nanotubes of thepresent disclosure are in the form of carbon nanotube bundles thatinclude a plurality of channels. In some embodiments, the carbonnanotube bundles have inter-tube spacings ranging from about 3 Å toabout 20 Å. In some embodiments, the carbon nanotube bundles haveinter-tube spacings of about 3.4 Å. In some embodiments, the carbonnanotube bundles have channels with sizes that range from about 5 Å toabout 20 Å. In some embodiments, the carbon nanotube bundles havechannels with sizes of about 6 Å.

The vertically aligned carbon nanotubes of the present disclosure canhave various angles. For instance, in some embodiments, the verticallyaligned carbon nanotubes of the present disclosure have angles thatrange from about 45° to about 90°. In some embodiments, the verticallyaligned carbon nanotubes of the present disclosure have angles thatrange from about 75° to about 90°. In some embodiments, the verticallyaligned carbon nanotubes of the present disclosure have an angle ofabout 90°.

The vertically aligned carbon nanotubes of the present disclosure canalso have various thicknesses. For instance, in some embodiments, thevertically aligned carbon nanotubes of the present disclosure have athickness ranging from about 10 μm to about 2 mm. In some embodiments,the vertically aligned carbon nanotubes of the present disclosure have athickness ranging from about 10 μm to about 1 mm. In some embodiments,the vertically aligned carbon nanotubes of the present disclosure have athickness ranging from about 10 μm to about 500 μm. In some embodiments,the vertically aligned carbon nanotubes of the present disclosure have athickness ranging from about 10 μm to about 100 μm. In some embodiments,the vertically aligned carbon nanotubes of the present disclosure have athickness of about 50 μm.

Substrates

In some embodiments, the vertically aligned carbon nanotubes of thepresent disclosure may be associated with a substrate (e.g., substrate40 in FIG. 1B). In some embodiments, the substrate also includes agraphene film (e.g., graphene film 38 in FIG. 1B). In some embodiments,the substrate serves as a current collector. In some embodiments, thesubstrate and the vertically aligned carbon nanotubes serve as a currentcollector.

Various substrates may be utilized in the electrodes of the presentdisclosure. For instance, in some embodiments, the substrate includes,without limitation, nickel, cobalt, iron, platinum, gold, aluminum,chromium, copper, magnesium, manganese, molybdenum, rhodium, ruthenium,silicon, tantalum, titanium, tungsten, uranium, vanadium, zirconium,silicon dioxide, aluminum oxide, boron nitride, carbon, carbon-basedsubstrates, diamond, alloys thereof, and combinations thereof. In someembodiments, the substrate includes a copper substrate. In someembodiments, the substrate includes a nickel substrate.

In some embodiments, the substrate includes a carbon-based substrate. Insome embodiments, the carbon-based substrate includes, withoutlimitation, graphitic substrates, graphene, graphite, buckypapers (e.g.,papers made by filtration of carbon nanotubes), carbon fibers, carbonfiber papers, carbon papers (e.g., carbon papers produced from grapheneor carbon nanotubes), graphene papers (e.g., graphene papers made byfiltration of graphene or graphene oxide with subsequent reduction),carbon films, metal carbides, silicon carbides, and combinationsthereof.

The vertically aligned carbon nanotubes of the present disclosure may beassociated with a substrate in various manners. For instance, in someembodiments, the vertically aligned carbon nanotubes of the presentdisclosure are covalently linked to the substrate. In some embodiments,the vertically aligned carbon nanotubes of the present disclosure aresubstantially perpendicular to the substrate. Additional arrangementscan also be envisioned.

Graphene-carbon Nanotube Hybrid Materials

In some embodiments, the vertically aligned carbon nanotubes of thepresent disclosure are in the form of graphene-carbon nanotube hybridmaterials. In some embodiments, the graphene-carbon nanotube hybridmaterials include a graphene film (e.g., graphene film 38 in FIG. 1B)and vertically aligned carbon nanotubes covalently linked to thegraphene film (e.g., vertically aligned carbon nanotubes 34 in FIG. 1B).In some embodiments, the vertically aligned carbon nanotubes arecovalently linked to the graphene film through carbon-carbon bonds atone or more junctions between the carbon nanotubes and the graphene film(e.g., junction 36 in FIG. 1B). In some embodiments, the verticallyaligned carbon nanotubes are in ohmic contact with a graphene filmthrough the carbon-carbon bonds at the one or more junctions. In someembodiments, the one or more junctions include seven-membered carbonrings. In some embodiments, the one or more junctions are seamless.

In some embodiments, the graphene-carbon nanotube hybrid materials ofthe present disclosure can also include a substrate that is associatedwith the graphene film (e.g., substrate 40 in FIG. 1B). Suitablesubstrates were described previously. For instance, in some embodiments,the substrate can include a metal substrate, such as copper. In someembodiments, the substrate includes a carbon-based substrate, such as agraphitic substrate. In some embodiments, the carbon-based substrate canwork both as a current collector and a carbon source for the growth ofcarbon nanotubes.

The graphene-carbon nanotube hybrid materials of the present disclosurecan include various graphene films. For instance, in some embodiments,the graphene film includes, without limitation, monolayer graphene,few-layer graphene, double-layer graphene, triple-layer graphene,multi-layer graphene, graphene nanoribbons, graphene oxide, reducedgraphene oxide, graphite, and combinations thereof. In some embodiments,the graphene film includes reduced graphene oxide. In some embodiments,the graphene film includes graphite.

The vertically aligned carbon nanotubes of the present disclosure mayalso be associated with graphene films in various manners. For instance,in some embodiments, the vertically aligned carbon nanotubes aresubstantially perpendicular to the graphene film (e.g., verticallyaligned carbon nanotubes 34 in FIG. 1B). In some embodiments, thevertically aligned carbon nanotubes of the present disclosure areassociated with graphene films at angles that range from about 45° toabout 90°.

The vertically aligned carbon nanotubes of the present disclosure can beprepared by various methods. For instance, in some embodiments, thevertically aligned carbon nanotubes of the present disclosure can bemade by: (1) associating a graphene film with a substrate; (2) applyinga catalyst and a carbon source to the graphene film; and (3) growingcarbon nanotubes on the graphene film.

In some embodiments, catalysts may include a metal (e.g., iron) and abuffer (e.g., alumina). In some embodiments, the metal (e.g., iron) andbuffer (e.g., alumina) can be grown from nanoparticles (e.g., ironalumina nanoparticles).

In some embodiments, the metal and buffer are sequentially depositedonto a graphene film by various methods, such as electron beamdeposition. In some embodiments, various carbon sources (e.g., ethene orethyne) may be deposited onto the graphene film by various methods, suchas chemical vapor deposition. In some embodiments, the graphene film canbe grown on a substrate from various carbon sources, such as gaseous orsolid carbon sources.

Additional embodiments of graphene-carbon nanotube hybrid materials andmethods of making the hybrid materials are described in an additionalPCT application by Applicants, which has been published as WO2013/119,295. The entirety of the aforementioned application isincorporated herein by reference.

Metals

The vertically aligned carbon nanotubes of the present disclosure maybecome associated with various metals. For instance, in someembodiments, the metals include, without limitation, alkali metals,alkaline earth metals, transition metals, post transition metals,rare-earth metals, and combinations thereof.

In some embodiments, the metals include alkali metals. In someembodiments, the alkali metals include, without limitation, Li, Na, K,and combinations thereof. In some embodiments, the metals include Li.

In some embodiments, the metals include alkaline earth metals. In someembodiments, the alkaline earth metals include, without limitation, Mg,Ca, and combinations thereof.

In some embodiments, the metals include transition metals. In someembodiments, the transition metals include, without limitation, Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Zn, and combinations thereof.

In some embodiments, the metals include post transition metals. In someembodiments, the post transition metals include, without limitation, Al,Sn, Sb, Pb, and combinations thereof.

Application of Metals to Vertically Aligned Carbon Nanotubes

Various methods may be utilized to apply metals to vertically alignedcarbon nanotubes. For instance, in some embodiments, the applying occursby filtration, ultrafiltration, coating, spin coating, spraying, spraycoating, patterning, mixing, blending, thermal activation,electro-deposition, electrochemical deposition, doctor-blade coating,screen printing, gravure printing, direct write printing, inkjetprinting, mechanically pressing, melting, and combinations thereof. Insome embodiments, the applying occurs by electrochemical deposition.

The application of metals to vertically aligned carbon nanotubes canoccur at various times. For instance, in some embodiments, the applyingoccurs during electrode fabrication. In some embodiments, the applyingoccurs after electrode fabrication.

In some embodiments, the applying occurs in situ during electrodeoperation. For instance, in some embodiments, electrodes that containthe vertically aligned carbon nanotubes of the present disclosure areplaced in an electric field that contains metals. Thereafter, the metalsbecome associated with the vertically aligned carbon nanotubes duringthe application of the electric field.

In some embodiments, the applying occurs by melting a metal (e.g., apure metal, such as lithium) over a surface of vertically aligned carbonnanotubes. Thereafter, the metals can become associated with thevertically aligned carbon nanotubes during the wetting of the verticallyaligned carbon nanotubes by the liquid metal.

In some embodiments, the applying occurs by electro-depositing a metal(e.g., a pure metal or a metal-containing solid material, such aslithium or lithium-based materials) over a surface of vertically alignedcarbon nanotubes. Thereafter, the metals can become associated with thevertically aligned carbon nanotubes during the electro-deposition. Insome embodiments, the metal may be dissolved in an aqueous or organicelectrolyte during electro-deposition.

Association of Metals with Vertically Aligned Carbon Nanotubes

The metals of the present disclosure can become associated withvertically aligned carbon nanotubes in various manners. For instance, asset forth previously, the metal can become associated with thevertically aligned carbon nanotubes in situ during electrode operation.In some embodiments, the metal can become reversibly associated with thevertically aligned carbon nanotubes. In some embodiments, the metal canbecome reversibly associated with the vertically aligned carbonnanotubes during electrode operation by association during charging anddissociation during discharging.

In some embodiments, the metals of the present disclosure can becomeassociated with vertically aligned carbon nanotubes in a uniform manner.For instance, in some embodiments, the metal becomes associated with thevertically aligned carbon nanotubes without forming dendrites. In someembodiments, the metal becomes associated with the vertically alignedcarbon nanotubes without forming aggregates (e.g., metal particulates ormossy aggregates).

The metals of the present disclosure can become associated with variousregions of vertically aligned carbon nanotubes. For instance, in someembodiments, the metal becomes associated with surfaces of thevertically aligned carbon nanotubes. In some embodiments, the metalforms a non-dendritic or non-mossy coating on the surfaces of thevertically aligned carbon nanotubes. In some embodiments, the metalbecomes infiltrated within the bundles of the vertically aligned carbonnanotubes.

In some embodiments, the metal becomes associated with the verticallyaligned carbon nanotubes in the form of a film. In some embodiments, thefilm is on the surface of the vertically aligned carbon nanotubes (e.g.,film 32 in FIG. 1B). Additional modes of associations can also beenvisioned.

Electrode Structures and Properties

The electrodes of the present disclosure can have various structures.For instance, in some embodiments, the electrodes of the presentdisclosure are in the form of films, sheets, papers, mats, scrolls,conformal coatings, and combinations thereof. In some embodiments, theelectrodes of the present disclosure have a three-dimensional structure.

The electrodes of the present disclosure can serve various functions.For instance, in some embodiments, the electrodes of the presentdisclosure can serve as an anode. In some embodiments, the electrodes ofthe present disclosure can serve as a cathode.

Different components of the electrodes of the present disclosure canserve various functions. For instance, in some embodiments, thevertically aligned carbon nanotubes serve as the active layer of theelectrodes (e.g, active layers of cathodes and anodes). In otherembodiments, the metals serve as the electrode active layer whilevertically aligned carbon nanotubes serve as a current collector. Insome embodiments, vertically aligned carbon nanotubes serve as a currentcollector in conjunction with a substrate (e.g., a copper substrateassociated with a graphene film). In some embodiments, the verticallyaligned carbon nanotubes of the present disclosure also serve tosuppress dendrite formation.

In more specific embodiments, the graphene-carbon nanotube hybridmaterials of the present disclosure serve as a current collector whilethe metal serves as an active material. In some embodiments, thegraphene-carbon nanotube hybrid materials of the present disclosureserve as a current collector in conjunction with a substrate.

The electrodes of the present disclosure can have various advantageousproperties. For instance, in some embodiments, the electrodes of thepresent disclosure have surface areas that are more than about 650 m²/g.In some embodiments, the electrodes of the present disclosure havesurface areas that are more than about 2,000 m²/g. In some embodiments,the electrodes of the present disclosure have surface areas that rangefrom about 2,000 m²/g to about 3,000 m²/g. In some embodiments, theelectrodes of the present disclosure have surface areas that range fromabout 2,000 m²/g to about 2,600 m²/g. In some embodiments, theelectrodes of the present disclosure have a surface area of about 2,600m²/g.

The electrodes of the present disclosure can also have high metalstorage capacities. For instance, in some embodiments, the electrodes ofthe present disclosure have metal storage capacities that are more thanabout 50 wt %. In some embodiments, the electrodes of the presentdisclosure have metal storage capacities that range from about 75 wt %to about 2,000 wt %. In some embodiments, the electrodes of the presentdisclosure have metal storage capacities ranging from about 600 wt % to700 wt %. In some embodiments, the electrodes of the present disclosurehave metal storage capacities of about 650 wt %. In some embodiments,the aforementioned weight percentages are represented as the mass ofdeposited metal divided by the mass of the vertically aligned carbonnanotubes.

The electrodes of the present disclosure can also have high specificcapacities. For instance, in some embodiments, the electrodes of thepresent disclosure have specific capacities of more than about 400mAh/g. In some embodiments, the electrodes of the present disclosurehave specific capacities of more than about 2,000 mAh/g. In someembodiments, the electrodes of the present disclosure have specificcapacities ranging from about 1,000 mAh/g to about 4,000 mAh/g. In someembodiments, the electrodes of the present disclosure have specificcapacities ranging from about 3,000 mAh/g to about 4,000 mAh/g. In someembodiments, the electrodes of the present disclosure have specificcapacities ranging from about 3,500 mAh/g to about 3,900 mAh/g.

The electrodes of the present disclosure can also have high arealcapacities. For instance, in some embodiments, the electrodes of thepresent disclosure have areal capacities ranging from about 0.1 mAh/cm²to about 20 mAh/cm². In some embodiments, the electrodes of the presentdisclosure have areal capacities ranging from about 0.4 mAh/cm² to about4 mAh/cm². In some embodiments, the electrodes of the present disclosurehave areal capacities of more than about 2 mAh/cm².

Incorporation Into Energy Storage Devices

The methods of the present disclosure can also include a step ofincorporating the electrodes of the present disclosure as a component ofan energy storage device. Additional embodiments of the presentdisclosure pertain to energy storage devices that contain the electrodesof the present disclosure.

The electrodes of the present disclosure can be utilized as componentsof various energy storage devices. For instance, in some embodiments,the energy storage device includes, without limitation, capacitors,batteries, photovoltaic devices, photovoltaic cells, transistors,current collectors, and combinations thereof.

In some embodiments, the energy storage device is a capacitor. In someembodiments, the capacitor includes, without limitation, lithium-ioncapacitors, super capacitors, micro supercapacitors, pseudo capacitors,two-electrode electric double-layer capacitors (EDLC), and combinationsthereof.

In some embodiments, the energy storage device is a battery (e.g.,battery 50 in FIG. 1C). In some embodiments, the battery includes,without limitation, rechargeable batteries, non-rechargeable batteries,micro batteries, lithium-ion batteries, lithium-sulfur batteries,lithium-air batteries, sodium-ion batteries, sodium-sulfur batteries,sodium-air batteries, magnesium-ion batteries, magnesium-sulfurbatteries, magnesium-air batteries, aluminum-ion batteries,aluminum-sulfur batteries, aluminum-air batteries, calcium-ionbatteries, calcium-sulfur batteries, calcium-air batteries, zinc-ionbatteries, zinc-sulfur batteries, zinc-air batteries, and combinationsthereof. In some embodiments, the energy storage device is a lithium-ionbattery.

The electrodes of the present disclosure can be utilized as variouscomponents of energy storage devices. For instance, in some embodiments,the electrodes of the present disclosure are utilized as a cathode in anenergy storage device (e.g., cathode 52 in battery 50, as illustrated inFIG. 1C). In some embodiments, the electrodes of the present disclosureare utilized as anodes in an energy storage device (e.g., anode 56 inbattery 50, as illustrated in FIG. 1C).

In some embodiments, the electrodes of the present disclosure include agraphene-carbon nanotube hybrid material that is utilized as an anode inan energy storage device. In some embodiments, the anodes of the presentdisclosure may be associated with various cathodes. For instance, insome embodiments, the cathode is a transition metal compound. In someembodiments, the transition metal compound includes, without limitation,Li_(x)CoO₂, Li_(x)FePO₄, Li_(x)NiO₂, Li_(x)MnO₂,Li_(a)Ni_(b)Mn_(c)Co_(d)O₂, Li_(a)Ni_(b)Co_(c)Al_(d)O₂, NiO, NiOOH, andcombinations thereof. In some embodiments, integers a,b,c,d, and x aremore than 0 and less than 1.

In some embodiments, cathodes that are utilized along with the anodes ofthe present disclosure include sulfur. In some embodiments, the cathodeincludes oxygen, such as dioxygen, peroxide, superoxide, andcombinations thereof. In some embodiments, the cathode contains metaloxides, such as metal peroxides, metal superoxides, metal hydroxides,and combinations thereof. In some embodiments, the cathode includeslithium cobalt oxide. In some embodiments, the cathode includes asulfur/carbon black cathode.

In some embodiments, the electronic devices that contain the electrodesof the present disclosure may also contain electrolytes (e.g.,electrolytes 54 in battery 50, as illustrated in FIG. 1C). In someembodiments, the electrolytes include, without limitation, non-aqueoussolutions, aqueous solutions, salts, solvents, additives, compositematerials, and combinations thereof. In some embodiments, theelectrolytes include, without limitation, lithium hexafluorophosphate(LiPF6), lithium (trimethylfluorosulfonyl) imide (LITFSI), lithium(fluorosulfonyl) imide (LIFSI), lithium bis(oxalate)borate (LiBOB),hexamethylphosphoustriamide (HMPA), and combinations thereof. In someembodiments, the electrolytes are in the form of a composite material.In some embodiments, the electrolytes include solvents, such as ethylenecarbonate, diethyl carbonate, dimethyl carbonate, ethyl methylcarbonate, 1,2-dimethoxyl methane, and combinations thereof.

The energy storage devices of the present disclosure can have variousadvantageous properties. For instance, in some embodiments, the energystorage devices of the present disclosure have high specific capacities.In some embodiments, the energy storage devices of the presentdisclosure have specific capacities of more than about 100 mAh/g. Insome embodiments, the energy storage devices of the present disclosurehave specific capacities ranging from about 100 mAh/g to about 2,000mAh/g. In some embodiments, the energy storage devices of the presentdisclosure have specific capacities ranging from about 100 mAh/g toabout 1,000 mAh/g. In some embodiments, the energy storage devices ofthe present disclosure have specific capacities of about 800 mAh/g.

The energy storage devices of the present disclosure can also have highenergy densities. For instance, in some embodiments, the energy storagedevices of the present disclosure have energy densities of more thanabout 300 Wh/kg. In some embodiments, the energy storage devices of thepresent disclosure have energy densities ranging from about 300 Wh/kg toabout 3,000 Wh/kg. In some embodiments, the energy storage devices ofthe present disclosure have energy densities ranging from about 1,000Wh/kg to about 2,000 Wh/ kg. In some embodiments, the energy storagedevices of the present disclosure have energy densities of about 1,840Wh/kg.

Additional Embodiments

Reference will now be made to more specific embodiments of the presentdisclosure and experimental results that provide support for suchembodiments. However, Applicants note that the disclosure below is forillustrative purposes only and is not intended to limit the scope of theclaimed subject matter in any way.

EXAMPLE 1 Carbon Nanotube-based Electrodes for Lithium-ion Batteries

In this Example, Applicants report a seamless graphene-carbon nanotube(GCNT) electrode that is capable of reversibly storing large amounts oflithium (Li) metal with complete suppression of dendrite formation. TheGCNT serves as a host material to insert and form Li as a thin coatingover its high surface area (˜2600 m² g⁻¹). With a Li storage capacity ofup to 4 mAh cm⁻² (823 mAh cm⁻³) and 25.3 Ah g⁻¹ _(G-CNT), the GCNTstores 6.6 times its weight in Li, which is 6.6 times greater thansilicon (Si). The capabilities, reversibility, and dendrite-free natureof the GCNT bode well for its use as a model structure for metal-basedanodes in secondary batteries.

Graphene was first grown via chemical vapor deposition (CVD) on a copper(Cu) substrate, followed by deposition of iron nanoparticles andaluminum oxide and subsequent CVD growth of carbon nanotubes (CNTs) at750° C. using acetylene as the carbon source (FIG. 2A). This method waspreviously shown by Applicants to produce CNTs that were covalently andseamlessly connected to the underlying graphene (FIG. 2B), providingohmic conductance between Cu and CNTs. See WO 2013/119,295.

CNTs were grown vertically from the Cu-graphene substrate as a 50 μmthick carpet (FIG. 2B). They exist in bundles (FIGS. 2C-D), which aresuperlattices held together by van der Waals interactions. In additionto an inter-tube spacing of ˜3.4 Å, the CNT bundles have 6 Å channels.The presence of formed CNTs were confirmed (FIG. 2F). In addition, theradial breathing modes (RBM) at 100 to 300 cm⁻¹ indicate single- tofew-walled CNTs (FIG. 2G).

Li is inserted into the highly porous and high surface area GCNT, wherethe morphology of the CNTs induce formation of Li on the CNT surfaces asa film or non-dendritic coating (FIG. 3A), slightly below 0 V vs Li/Li⁺(FIG. 3B). Reversible Li insertion and extraction from the GCNT areobserved (FIG. 3B). These are confirmed by GCNT color change from blackto silver, indicating formation of Li metal (FIG. 3C), and back to blackupon Li extraction.

Scanning electron microscopy (SEM) images of the lithiated GCNT(GCNT-Li) (FIGS. 3D-E) show that Li is not deposited atop the GCNT as aseparate film, but is rather inserted into the pillared CNT structure.The absence of Li aggregation or particulates deposited in themicrometer-sized pores of the GCNT-Li (FIG. 3F) suggests either Liformation on the surface of CNT bundles or penetration into the CNTbundles to form on individual CNTs. Moreover, the relatively roughsurface of the CNT bundles shows the presence of a thin layer of film,clearly indicating that Li is formed on the CNT surfaces.

The base-view SEM image (FIG. 3G) also indicates a similarly roughsurface of the CNT bundles and the presence of a deposited film, whichunderscores the significance of the micrometer-sized pores in Li iondiffusion through the GCNT. No discernable exfoliation of the CNTbundles in the delithiated GCNT (FIGS. 3H-I) is observed.

In FIGS. 3J-K, the transmission electron microscopy (TEM) images of thelithiated CNTs show deposition in the form of nanoparticles on thesurface of the CNTs. The SEM images of the GCNT-Li presented in FIGS.3D-I were recorded after 250 cycles and they show no evidence offormation of dendritic, mossy, and related structures that have hinderedapplication of Li metal anodes.

In contrast, deposition over flat substrates (graphene-covered copperfoil, CuG) as shown in FIG. 3L produces irregular deposits of Li (FIGS.3M-N). Mossy structures are observed in less than 10 cycles. In thethree-dimensional, high surface area GCNT, there is enormous surfacearea for Li to deposit without dendritic/mossy Li formation. Theporosity facilitates Li ion diffusion in and out of the GCNT.

FIG. 4A shows representative curves of the Li insertion and extractionfrom the 6th cycle. The discharge capacity of the GCNT-Li is 3920mAh g⁻¹with a coulombic efficiency of 94.3%. An areal capacity of 2 mAh cm⁻² isobtained from 50 μm thick GCNT. The first cycle coulombic efficiency is˜60%. The discharge and charge curves are characterized by remarkablyflat voltages at −50 mV and 50 mV, respectively (FIG. 4A). The voltageprofile of the GCNT-Li resembles that of Li metal directly plated on acurrent collector, having a characteristic flat charge/discharge profileclose to 0 V (FIG. 5).

It is evident that the inserted Li in the GCNT is metallic in contrastwith Li-intercalated graphite where the Li forms a well-definedintercalation compound (LiC₆) with graphite and exists as an ion.Additionally, previously reported insertion of Li into CNTs have hadlimited promise toward developing practical LIBs because the voltageprofile was not flat and the electrode needed to be charged above 3 V toreversibly extract much of the inserted Li (FIG. 6). The flat voltagehere is observed over 200 hours of continuous cycling (300 cycles)(FIGS. 4B and 7).

In comparison, Li deposited directly on Cu-graphene shows oscillatingcoulombic efficiency and increased polarization (FIG. 4C), in additionto the problematic morphology of Li formed on the bare Cu-graphenesubstrate (FIGS. 3L-N). After 300 cycles, there is no capacity fading,and the coulombic efficiency is 99.83% (FIG. 4D). The concentratedelectrolyte, 4 M lithium bis(fluorosulfonyl)imide in1,2-dimethoxyethane, was reported to promote high coulombic efficiencyin Li metal anodes due to decreased reactive solvent amount andincreased Li⁺ concentration.

A control experiment was carried out to compare the seamless monolithicGCNT grown on Cu relative to CNTs randomly dispersed on Cu. While theGCNT maintains a flat voltage profile over many cycles, the horizontallydeposited CNT exhibits oscillating, unstable voltage cycles (FIGS. 8A-Band 9).

The specific capacity of the GCNT-Li is tunable by a time-controlledconstant current Li insertion up to 4 mAh cm⁻² (25.3 Ah g⁻¹ _(G-CNT))(FIG. 9A). GCNT-Li electrodes with capacities from 0.4 to 4 mAh cm⁻² (2to 25.3 Ah g⁻¹ _(G-CNT)) are shown with flat voltage profiles anddendrite-free Li insertion (FIGS. 9A and 10). The large areal capacitydemonstrates the high volumetric capacity (FIG. 10). A small voltage gapof 100 mV between the Li insertion and extraction curves is observed for0.7 mAh cm⁻²(4.4 Ah g⁻¹ _(G-CNT)), increasing to 200 mV at 4 mAhcm⁻²(25.3 Ah g⁻¹ _(G-CNT)), likely due to the thicker inserted Li orpossible thicker solid electrolyte interphase (SEI) layer.

With a capacity of 25.3 Ah g⁻¹ _(G-CNT) (FIG. 9B), the GCNT stores 6.6times its weight in Li, 68 times greater than does graphite (372 mAh g⁻¹_(C)), and 6.6 times greater than does Si (3859 mAh g⁻¹ _(Si)). Thecapacity also exceeds other Li storage materials. With the mass of Liincluded in computing the capacity, the GCNT-Li has a capacity of 3351mAh g⁻¹ _(GCNT-Li), which is very close to the theoretical capacity ofLi (3860 mAh g⁻ _(LiC6)). In this regard, the GCNT-Li (3351 mAh g⁻¹_(GCNT+Li)) has 1.8 times higher Li content than Li₁₅Si₄ (1857 mAh g⁻¹_(Li15Si4)), and 9.9 times higher Li content than LiC₆ (339 mAh g⁻_(LiC6)) (FIG. ⁹C).

The GCNT-Li electrode exhibits high specific capacity, both areal andgravimetric, under increased current densities. In FIG. 9D, the GCNT isshown to insert and extract Li to a rate as high as 10 mA cm⁻² (58 A g⁻¹_(G-CNT)), producing a capacity of ˜0.7 mAh cm⁻² (4.4 Ah g⁻¹ _(G-CNT)),which is independent of the current density. The flatness of the curvesis still maintained up to 4 mA cm⁻² (23 A g⁻¹ _(G-CNT)). However, duringthe GCNT-Li cycling at 10 mA cm⁻² (58 A g⁻¹), a significant polarizationis observed from the Li insertion/extraction curves with loss of thecharacteristic flatness at lower current densities.

As shown in FIG. 9E, the GCNT-Li maintains a very high coulombicefficiency and good cycle stability at high current densities. The highcurrent capability supersedes values reported on other LIB electrodes.Moreover, the optimal electrical conductivity of the GCNT monolithfacilitates electron transport without the need for conductiveadditives. The seamless growth of CNTs on graphene, where the grapheneis grown in intimate contact with the Cu, eliminates theelectrode-current collector resistance. The vertical carpet nature ofthe CNTs would enhance Li-ion diffusion through non-tortuous Liinsertion and extraction with flexible CNT movements.

In a further experiment, excess Li was inserted into the GCNT until 5mAh cm⁻² was attained (FIG. 11A). The electrode was then delithiated andlithiated for 5 cycles to stabilize the coulombic efficiency. TheGCNT-Li was then allowed to undergo Li insertion/extraction cycles up toa capacity of 1 mAh cm⁻² (FIG. 11B), yielding an excess Li equivalent of4 mAh cm⁻². This significantly improved the cycle life of the electrodewith no sign of decline after 500 cycles and a coulombic efficiency of100% (FIGS. 11C-D).

In addition, the GCNT-Li anode was combined with a sulfur cathode toproduce a full Li-sulfur battery. The areal capacity of the GCNT-Li wasmatched with that of the sulfur cathode. As shown in FIG. 12, the twocharacteristic plateaus of sulfur lithiation appear at 2.3 and 2.1 V.The resulting sulfur lithiation products (lithium polysulfides) areknown to diminish the cycle life of Li-sulfur batteries because theyreact with the Li metal anode, such as those inserted in the GCNT-Li.

Thus, a layer of graphene nanoribbons was deposited on the separator torestrain the polysulfides to the cathodic side, thereby improving thestability of the battery. Additionally, a small voltage gap of 190 mVbetween the charge and discharge of the full-cell is observed. Thebattery delivers a specific capacity of 800 mAh g⁻¹ (2 mAh cm⁻²), whichfar exceeds the theoretical capacity of ˜100mAh g⁻¹ in a graphite/LiCoO₂system. This high capacity, despite the relatively low voltage featureof the sulfur cathode, enables a full battery with a high energy densityof ˜1840 Wh kg⁻¹, more than 6 times higher than 300 Wh kg⁻¹ forgraphite/LiCoO2 cells.

In addition, a full battery made from GCNT-Li and LiCoO2 is demonstrated(FIG. 13). The gravimetric energy density is 310 Wh kg⁻¹ for the firstcycle discharge.

EXAMPLE 1.1 GCNT Preparation

The preparation of GCNT was similar to the previously reported methods.See WO 2013/119295. First, Bernal-stacked multilayer graphene was grownon copper foil (25 μm) using the CVD method, as reported elsewhere. Thecatalysts for CNT growth were deposited by e-beam evaporation over thegraphene/Cu foil to form graphene/Fe (1 nm)/Al₂O₃ (3 nm). The CNT growthwas conducted under reduced pressure using a water-assisted CVD methodat 750° C. First, the catalyst was activated by using atomic hydrogen(H.) generated in situ by H₂ decomposition on the surface of a hotfilament (0.25 mm W wire, 10 A, 30 W) for 30 seconds under 25 Torr (210sccm H₂, 2 sccm C₂H₂ and water vapor generated by bubbling 200 sccm ofH₂ through ultra-pure water). After the activation of the catalyst for30 seconds, the pressure was reduced to 8.3 Torr and the growth wascarried out for 15 minutes.

EXAMPLE 1.2 Electrochemical Insertion (and Extraction) of Li Into GCNT

The electrochemical reaction was performed in 2032 coin-type cells usingGCNT substrates and Li foil as both counter and reference electrodes.The GCNT substrates are circular with total area of ˜2 cm². Theelectrolyte used was 4 M lithium bis(fluorosulfonyl)imide (LiFSI)(Oakwood Inc.) in 1,2-dimethoxyethane (DME). The LiFSI salt was vacuumdried (<20 Torr) at 100° C. for 24 hours and DME was distilled over Nastrips. All the experiments were conducted inside a glove box withoxygen levels below 5 ppm. The separator was Celgard membranes K2045.

Previous to the coin cell assembly, the GCNT substrate was prelithiatedby putting one drop of electrolyte on the surface of GCNT, pressing a Licoin gently against the GCNT and leaving it with the Li coin on top for3 hours. Adding excessive amounts of the electrolyte solution during thepretreatment was found to yield ineffective prelithiation due to poorcontact between the GCNT and the Li. After the prelithiation, the GCNTwas assembled in a coin cell using the same Li chip used in theprelithiation. The current density for the electrochemical measurements(insertion/extraction and cycling) ranges from 1 to 10 mA cm ², allperformed at room temperature. For the Li plating (discharging process),a time-controlled process with a constant current regime was appliedwith no cut-off voltage limit. The stripping process (charge process)was set to a constant current regime with a cut-off voltage of 1 V (vsLi⁺/Li). A control experiment was carried out using a copper foil uponwhich graphene is grown by CVD.

EXAMPLE 1.3 Materials Characterization

Coin cells were dissembled inside a glove box to check the morphology ofthe GCNT electrodes after Li insertion/extraction. SEM images of theGCNT electrodes were obtained with an FE-SEM (JEOL-6500F) at anaccelerating voltage of 20 kV. High resolution TEM (HRTEM) images (JEOLFEG-2100F) were obtained after preparing the samples by sonicating theGCNT substrate in acetonitrile and dropping the dispersion over TEMgrids.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present disclosure to itsfullest extent. The embodiments described herein are to be construed asillustrative and not as constraining the remainder of the disclosure inany way whatsoever. While the embodiments have been shown and described,many variations and modifications thereof can be made by one skilled inthe art without departing from the spirit and teachings of theinvention. Accordingly, the scope of protection is not limited by thedescription set out above, but is only limited by the claims, includingall equivalents of the subject matter of the claims. The disclosures ofall patents, patent applications and publications cited herein arehereby incorporated herein by reference, to the extent that they provideprocedural or other details consistent with and supplementary to thoseset forth herein.

What is claimed is:
 1. A lithium-metal battery comprising: a cathode; anelectrolyte in contact with the cathode; and an anode in contact withthe electrolyte opposite the cathode, the anode including: carbonnanotubes; and a metallic-lithium coating over and between the carbonnanotubes.
 2. The lithium-metal battery of claim 1, the carbon nanotubesand the metallic-lithium coating over and between the carbon nanotubeshaving a lithium content greater than 339 mAh per combined gram ofmetallic-lithium and carbon content.
 3. The lithium-metal battery ofclaim 2, the carbon nanotubes and the metallic-lithium coating over andbetween the carbon nanotubes having lithium content greater than 1,857mAh per combined gram of metallic-lithium and carbon content.
 4. Thelithium-metal battery of claim 1, wherein an amount of the metalliclithium is a function of a charge of the lithium-metal battery.
 5. Thelithium-metal battery of claim 1, the cathode comprising sulfur.
 6. Thelithium-metal battery of claim 5, further comprising at least one layerof graphene between the cathode and the anode.
 7. The lithium-metalbattery of claim 6, the layer of graphene comprising graphenenanoribbons.
 8. The lithium-metal battery of claim 1, further comprisinga substrate supporting the carbon nanotubes opposite themetallic-lithium coating.
 9. The lithium-metal battery of claim 8,further comprising a graphene layer between the substrate and the carbonnanotubes.
 10. The lithium-metal battery of claim 9, wherein the carbonnanotubes are in ohmic contact with the graphene layer.
 11. Thelithium-metal battery of claim 1, wherein the electrolyte hasconcentrated lithium salts.
 12. The lithium-metal battery of claim 11,wherein the electrolyte has a lithium concentration of 4 mol L⁻¹. 13.The lithium-metal battery of claim 1, the anode having a specificcapacity greater than 1,000 mAh/g.
 14. An electrode comprising: asubstrate; graphene overlaying the substrate; carbon nanotubes extendingfrom and in ohmic contact with the graphene; and a non-dendritic coatingof a metal over and between the carbon nanotubes.
 15. The electrode ofclaim 14, wherein the metal comprises lithium.
 16. The electrode ofclaim 14, wherein the substrate comprises copper.
 17. The electrode ofclaim 14, wherein the metal consists essentially of lithium.
 18. Theelectrode of claim 14, wherein the carbon nanotubes are aligned.
 19. Theelectrode of claim 14, wherein the carbon nanotubes are in a form of anarray.
 20. The electrode of claim 14, wherein the carbon nanotubes arein the form of random networks.
 21. The electrode of claim 14, whereinthe graphene comprises graphene nanoribbons.
 22. The electrode of claim14, wherein the non-dendritic coating lacks mossy aggregates.
 23. Theelectrode of claim 14, wherein the non-dendritic coating is infiltratedwithin bundles of the carbon nanotubes.
 24. The electrode of claim 14,wherein the electrode is an anode, the non-dendritic coating formed bydepositing metal ions from a cathode to the anode.
 25. An electrodecomprising: a carbon-based substrate, wherein the carbon-based substrateis selected from the group consisting of a network of graphiticsubstrates, carbon fibers, graphene, graphene nanoribbons, carbonnanotubes, and combinations thereof; carbon nanotubes extending from andin ohmic contact with the carbon-based substrate; and a non-dendriticcoating of a metal over and between the carbon nanotubes that areextending from and in ohmic contact with the carbon-based substrate.